Add method declarations and interface dispatch to Scriggo

Normalized profile

What this task asks for

Implement method declarations with receiver handling, method expressions, and interface satisfaction for Scriggo-defined types. Scriggo rejects method declarations on user-defined types. When an addressable value has only a pointer receiver method, auto-address-taking must apply. Named and unnamed receiver forms must be supported. Support method expressions: `T.ValueMethod` and `(*T).PtrMethod` must produce callable function values usable in any expression context including direct calls. Using `T.PtrMethod` where the method has a pointer receiver must produce a compile error. Support interface satisfaction: a Scriggo-defined type whose method set matches a Go interface must satisfy that interface, and method calls through interface variables must dispatch to the correct Scriggo method implementation at runtime.